Apparatus for communication systems



Feb. 4, .1936. A. J. SORENSEN APPARATUS FOR COMMUNICATIQN SYSTEMS Filed July '11, 1954 TA Transmitting p Apparatus M71 02?! i Commzmz'caizhg 12 45 2 fi Amplifier Y 1 gZzer 1 ;1 n 0dalaioP LS Receiving Apparatus INVENTOR Andrewi SOPQHSQI) HIS ATTORNEY Patented Feb. 4, 1936 UNITE QFFICE APPARATUS FOR COMZM'UNIGATION SYSTEMS Application July 11, 1934, Serial No. 734,654

2 Claims.

My invention relates to apparatus for communication systems, and particularly to apparatus for carrier telephone systems for railway trains.

I will describe one form of apparatus embody- 5 ing my invention, and will then point out the novel features thereof in claims.

A feature of my invention is the provision in systems of the type referred to of a plurality of inductor coils which are mounted in inductive relation with the communicating channel and each of which coils is included in a circuit tuned to resonance at a distinctive frequency within the frequency spectrum, the resonant frequency of the different circuits being frequencies which differ from each other. In other words, the tuning of the circuits for the different inductors is staggered along the frequency spectrum. Staggered tuning, when referred to in the following description, will, therefore, be understood to mean tuning the different inductor coils and circuits therefor to resonance at different frequencies spaced apart within the band it is desired to transmit. Other features and advantages of my invention will appear as the specification progresses.

For a better understanding of my invention reference may be had to the accompanying drawing which is a diagrammatic View of one form of apparatus embodying my invention for a railway train telephone system.

Communication systems have been proposed for telephone communication from a station located on a vehicle of a railway train with a wayside station or with a station located on a vehiole of another train or with a station located on a second vehicle of the same train by transmitting between the two stations a carrier current modulated with voice frequencies, the communication channel preferably including the traffic rails as disclosed in the United States application for Letters Patent Serial No. 450,135, filed May 6, 1930, by Lars O. Grondahl, for Electric train signaling systems. In such systems a station in sending out current supplies the current to the trafiic rails through the medium of a circuit electrically coupled therewith, the current flowing in both directions from the point where it is supplied to the rails and returning through the ground. Current is picked up at the receiving station through the medium of a circuit electrically coupled with the trafiic rails.

In such systems the transmitting apparatus at each station is normally inactive and is energized and placed in circuit only during the sending of current from that station. The receiving appa- -loud speaker reduced to a low level.

ratus at each station is normally active and in circuit ready to receive a message from the remote station at any time, and since it preferably includes a loud speaker and a high gain amplifier, small earth currents and stray magnetic 5 fields picked up during non-communicating periods may produce a noise that sometimes becomes annoying. It has been proposed to use air core inductor coils on the train having induction with the trafiic rails for inducing an elec- 0 tromotive force in the rails when connected with the transmitting apparatus and for inductively receiving an electromotive force due to current flowing in the rails when connected with the receiving apparatus. Such air core inductor coils 5 should be preferably constructed with a relatively low power factor and should be included in a circuit sharply tuned in order that noise currents and unwanted energy will be ineffective to create voltages of operative magnitude and noise at the 20 Air core inductor coils when thus constructed and arranged are effective, however, to pass only a narrow band of the voice frequencies of a telephone current, the band edge frequencies being very weak and 25 the resulting speech distorted and unintelligible. To provide transmission of a voice frequency band having a width sufficient for telephone communication and wherewith variations in strength between the band edge frequencies and the mid 3O frequencies is within limits necessary to assure readily intelligible speech I provide a plurality of low power factor air core coils having staggered tuning along the voice spectrum.

To fix the ideas, I shall assume that a band of voice frequencies extending from 500 cycles to 2500 cycles per second for telephoning is desired,

a carrier of 7000 cycles per second is provided and that single band transmission is contemplated, the upper side band being utilized. It 40 follows that for telephone communication a band of frequencies extending from 7500 to 9500 cycles is transmitted. It will be understood, of course, that my invention is not limited to these specific frequencies and that other frequencies may be 5 chosen if found desirable.

The transmitting apparatus will ordinarily include a microphone, a generator of carrier current, means for modulating the carrier with frequencies produced by the voice impulses in the microphone, means for suppressing the carrier and one side band and an amplifier for amplifying the outgoing current to a relatively high energy level. The receiving apparatus will ordinarily include, in addition to the high gain reference character M and the carrier generator,

modulator and transmitting amplifier are. indicated conventionally at TA since, as stated above, these latter devices form no part of my present invention and may take any of several forms well known to the art. The microphone Mis preferably carried during non-communicating periods in a rack not shown and out of which it may be lifted when it is desired to establish a telephone conversation. 'To' facilitate the handling of the microphone it is mounted on a handle l5 which is capable of being manually operated to a normal and a communicating position, these positions being indicated by dotted lines in the drawing. As shown schematically, a contact I6 is operatively connected with the handle. l5 and is moved tothe two positions designated by the numerals l and 2 in response to the normal and communicating positions, respectively. A push button I! is mounted on the handlev !5, the contact member [8 of which push button is adapted to make engagement with a contact i9 when the push button is depressed and to break engagement therewith when the push button is released.

The microphone M is connected with the. input of the transmitting apparatus TA' over wires l0 and II, while the wires I2 and I3 connect the output of the transmitting apparatus with the winding 14 of a transformer Tl, the front contacts 15'|9 and ll-80 of a directional relay-DR tobe referred to later being interposed in the wires l2 and I3. It is deemed sufiicient for this description to say that frequencies corresponding to the voice frequencies produced in the microphone will be applied to-the carrier, which in this instance is of 7000 cycles per second, for modulating thecarrier, the carrier and the lower side band will be suppressed, and the upper side band will be amplified to a relatively high energy level and supplied to the winding l4 of the transformer Tl when the directional relay is energized, the

current in the winding 14 being in turn effective to induce electromotive forces of corresponding frequencies in transmitting circuits to be described more fully hereinafter.

The equipment includes a directional relay DR which is here shown as a direct current neutral relay adaptable of being energized by direct current from any convenient source such as a battery not shown. The directional relay DH is provided with a simple energizing circuit which includes the No. 2 position of the contact l6 and the push button l1 depressed. That is to say, the directional relay is normally deenergized and is energized when the handle I5 is moved to the communicating position and the push button I? is depressed. v

The receiving apparatus shown conventionally by the reference character RA consists, as stated hereinbefore, of an amplifier, demodulator and afilter, each of which devices may take any one of several forms well known to the art. The input of the receiving apparatus RA is connected with the winding 14 of the transformer Tl over the back contacts 'l5'l6 and Tl'l8 of the directional relay DR, the output of the receiving apparatus being connected with the winding of the loud speaker LS. It is deemed sufiicient for this description to say that a side band carrier telephone current supplied to the input of the bandpass filter of the receiving apparatus will be passed to the input of the amplifier and demodulator where it will be amplified and the audio speaker.

Four separate air core low power factor inductor windings are provided, which may take different forms and construction and which may be mounted on the vehicle at any convenient place in inductive relation with the traific rails 4.and"4 As here shown, each winding is made up of two substantially equal portions one associated'with each rail. 65 and 05 are two portions of one winding, the portion 65 being positioned above and on the outside of rail 4 and the portion I55 being positioned above and on the outside of rail 4 With a condenser 60 are serially connected across the winding 61 of the transformer TI to form a circuit which is tuned to resonance at say about 7750 cycles, and which is so proportioned that the circuit is provided with a relatively low power factor, say, for example, of about 1.5% at frequencies of the order of 10,000 cycles. 68 and 68 are two portions of a second winding, the portion 58 being positioned above and on the inside of the rail 4 and the portion 08 being positioned above and on the inside of the rail l and this winding Gib-58* is connected across the transformer winding 6'5 in series with a condenser 69 toform a circuit which is tuned to resonance at the frequency of say 8250 cycles, the parts of this circuit being further so proportioned that as in.

the case above a circuit power factor of about 1.5% is established. Again, 10 and 10 are the two portions of a third winding connected across the transformer winding 01, a condenser H being interposed in the connection for tuning the circuit thus formed to resonance at a frequency of say 8750 cycles, and for providing the circuit with a power factor of substantially 1.5%. A fourth winding is associated with the traffic rails and consists of the two portions 12 and 12 the two:

portions being connected across the transformer winding 57 in series with a condenser 13. The parts of this-last circuit are so proportioned as to tune the circuit to resonance at say about 9250 cycles and to provide a circuit power factor of about 1.5%. It follows that each of these four windings will pass its own part of the voice frequency band to the transformer winding 61, the maximum of transmission occurring at the frequencies at which the different circuits are tuned to resonance and a minimum occurring roughly halfway between such frequencies. It will be clear that the resultant transmission obtained from the plurality of air core low powerfactor coils with staggered tuning will produce a high energy transmission over the entire voice spectrum and variation in strength of the frequencies near the band edges with respect to the mid frequencies will be small, Electromotive forces of frequencies corresponding to the frequencies of the currents supplied to the transformer winding 61 will be induced in the winding 14 of that transformer which, in turn, will be supplied to the receiving apparatus over the back contacts frequencies reproduced and supplied to the loud The two portions 05 and 65* together 15-16 and "-18 of the directional relay DR. At such time as the directional relay DR is picked up and the winding 14 of the transformer Tl transferred from the receiving apparatus to the output of the transmitting apparatus, and a side band telephone current is supplied to the winding 14, electromotive forces of corresponding frequencies will be induced in the winding 61 of the transformer. Each of the four separate air core inductors will now be effective to transmit its frequency of the telephone current to the traflic rails with the result that the resultant transmission obtained from the plurality of air core coils with staggered tuning will be of a relatively high level for the entire frequency band.

The operation of the apparatus may be described as follows: During non-communicating periods the microphone M will be placed in the rack, the handle IE will be set at the normal position and the directional relay DR will be deenergizedi Under these circumstances the four separate air core inductor coils will be effective to receive a side band carrier telephone current having a width extending from 7500 to 9500 cycles which telephone current will be passed through the transformer TI to the input of the band-pass filter of the receiving apparatus and thence to the amplifier and demodulator, the audio frequencies being in turn supplied to the loud speaker. The staggered tuning of the separate inductor coils i will be operative to pass the entire band of frequencies with the strength of the band edge frequencies only a little less than that of the mid frequencies. To send a telephone current during a conversation, the handle 15 will be moved to the communicating position and the push button I? will be depressed to pick up the directional relay DR. Voice frequencies now produced in the microphone M will be translated to the upper side band of the carrier and supplied to the 'winding 14 of the transformer to induce electromotive force of corresponding frequencies in the winding 61. The four separate air core inductor coils with staggered tuning will now be operative to effectively induce in the traffic rails frequencies over the entire band extending from 7500 to 9500 cycles.

I have here described my invention as applied to a railway train telephone system, it will be understood, however, that I do not wish to limit myself to such systems, and my invention is equally useful to other communication systems employing a current having a desired frequency band.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scopeof the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination with railway train-carried telephone apparatus comprising transmitting apparatus including a microphone and a generator for supplying a carrier telephone current and receiving apparatus including a demodulator and a loud speaker capable of reproducing the audio frequencies of a carrier telephone current, a first circuit on a train including a winding and a condenser tuned to resonance at a first predetermined frequency of the carrier telephone current, a second circuit on the train including a winding and a condenser tuned to resonance at a second predetermined frequency of said telephone current, a relay, another winding electrically coupled with both said first and second circuits, a first circuit means for coupling said other winding with the output of the transmitting apparatus including a front contact of said relay, a second circuit means for coupling said other winding with the input of the receiving apparatus including a back contact of said relay, and manually controlled means for governing said relay.

2. In combination with railway train-carried telephone apparatus comprising transmitting apparatus including a microphone and a generator for supplying a carrier telephone current and receiving apparatus including a demodulator and a loud speaker capable of reproducing the audio frequencies of a carrier telephone current, a communication circuit including the traffic rails, a first circuit on a train including a winding and a condenser tuned to resonance at a first predetermined frequency of the carrier telephone current, said winding inductively coupled with the traffic rails, a second circuit on the train including a winding and a condenser tuned to resonance at a second predetermined frequency of said telephone current, said winding inductively coupled with the traflic rails, a relay, a first circuit means connected with the transmitting apparatus including a front contact of the relay and a winding coupled with both said first and second circuits for inducing in the trafiic rails electromotive forces having frequencies corresponding to the carrier telephone current, a second circuit means connected with the receiving apparatus including a back contact of the relay and a winding effectively influenced by both said first and second circuits for supplying to the receiving apparatus electromotive forces corresponding to a desired band width of frequencies of a carrier telephone current flowing in the traffic rails with variation in strength of the band edge frequencies and the mid frequencies within the limits necessary for readily intelligible speech, and manually controlled means for governing the relay.

ANDREW J. SORENSEN. 

